The invention relates to excavators and to machines for material transfer comprising an element movable via at least one hydraulic cylinder.
With excavators and machines for material transfer such as excavators, wheel-mounted loaders and similar plant, a boom and/or a shaft are moved e.g. via two parallel hydraulic cylinder pairs. In the case of an excavator, an attachment tool is then attached to the shaft and the good to be loaded is transferred with it. Both the boom and the shaft and the attachment tools naturally have masses. This means that only a small part of the energy used for the lifting work benefits the lifting of the load. The much greater part must be used for the lifting of the equipment and of the attachment tool.
A detail of an excavator and of machines for material transfer in accordance with the prior art is shown by way of example in FIG. 1. It is an excavator in the present case. A boom 12 is hinged to a rotating deck 10 of an excavator here and is movable via two hydraulic cylinder pairs 14. The hydraulic cylinder pairs are connected together, as can be seen from the hydraulic circuit diagram in accordance with FIG. 1a. 
Some first efforts have already been made to recover the energy expended in the lifting work of the equipment and of the attachment tool in an energy recovering system. For this purpose, it was attempted, for example in DE 102 56 442 A1 and DE 103 15 071 A1, to feed hydraulically stored energy into the main hydraulic circuit. However, this is only successful with limitations since the infeed pressure must always be larger than the system pressure in the main circuit.